Tagma ( Latin tagma , plural tagmata from the Greek. Τάγμα ) is the body division in segmented ( jointed ) animals. As a rule, a tagma is considered to be each more or less isolated part of the body, consisting of several relatively homogeneous segments. In different groups, the number of tagm and their segmental composition is different. The most widely known examples of tagmas are: the head, chest and abdomen of insects , cephalothorax and the “abdomen” (opistosome) of spiders . This concept is mainly used to describe the structure of annelids and arthropods .
Tagmosis
Tagmosis (or tagmatization) is the tendency to distinguish groups of segments that have a similar structure, perform a similar function and carry limbs close in structure. The simplest manifestation of tagmosis is the division of the body into the front head and back trunk. This simple and most ancient version of the structure of arthropods has been modified in almost all modern taxa. In representatives of most of them, the trunk was divided into the thoracic and abdominal sections. The result was the formation of three tagms. In a number of arthropods, some or all of the thoracic segments combined with the head and formed a secondary tagma - cephalothorax . In all insects, the body is subdivided into the head, chest, and abdomen. At the same time, the chelicerae have a cephalothorax and abdomen, and in crustaceans the composition of all three tagms can vary significantly. Representatives of three large taxa underwent tagmosis independently of each other. Accordingly, the departments of their body are not homologous , despite the fact that they have the same name.
Literature
- Zoology of Invertebrates / Ed. W. Westheide and R. Rieger. - M. , 2008.